Solar power system and heat exchanger

ABSTRACT

The disclosed solar power system includes an oil circuit, a molten salt circuit, and a heat exchanger in communication with both the oil and molten salt circuits. The disclosed heat exchanger includes at least one heat pipe, the ends of which are within first and second plenums provided by spaced-apart housings.

BACKGROUND

Solar power systems, or plants, are known and used for capturing solar energy and generating electricity. The system typically includes one or more solar collectors that direct solar energy into a heat-absorbing fluid, such as a synthetic oil. The heated fluid is used in a thermodynamic cycle to produce steam that drives a turbine to generate electricity. In some systems, a molten salt absorbs and stores heat from the heat-absorbing fluid via a heat exchanger.

SUMMARY

A heat exchanger according to an exemplary aspect of the present disclosure includes, among other things, at least one heat pipe having a first end and a second end. The heat exchanger further includes a first housing including a first plenum, the first end of the at least one heat pipe within the first plenum. Also included is a second housing including a second plenum. The second end of the at least one heat pipe is within the second plenum, and the second housing is spaced from the first housing to provide a double-layer boundary between the first plenum and the second plenum.

In a further non-limiting embodiment of the foregoing heat exchanger, the first plenum is in communication with a first fluid, and the second plenum is in communication with a second fluid different from the first fluid.

In a further non-limiting embodiment of the foregoing heat exchanger, the first and second fluids are reactive when brought together.

In a further non-limiting embodiment of the foregoing heat exchanger, the first fluid is oil and the second fluid is a molten salt.

In a further non-limiting embodiment of the foregoing heat exchanger, the at least one heat pipe has a working fluid contained therein.

In a further non-limiting embodiment of the foregoing heat exchanger, the working fluid is non-reactive with oil and molten salt.

In a further non-limiting embodiment of the foregoing heat exchanger, the heat pipe has a longitudinal axis, and the first and second housings are spaced apart along the longitudinal axis of the heat pipe.

In a further non-limiting embodiment of the foregoing heat exchanger, the first and second ends are closed ends.

A solar power system according to an exemplary aspect of the present disclosure includes, among other things, a concentrated solar receiver, an oil circuit, a molten salt circuit, and at least one heat exchanger in communication with both the oil circuit and the molten salt circuit. The at least one heat exchanger includes a first housing including a first plenum in communication with the oil circuit, and a second housing including a second plenum in communication with the molten salt circuit. The first housing is spaced from the second housing to provide a double-layer boundary between the first plenum and the second plenum.

In a further non-limiting embodiment of the foregoing solar power system, the at least one heat exchanger includes at least one heat pipe having a first end within the first plenum and a second end within the second plenum, and the first and second ends are closed ends.

In a further non-limiting embodiment of the foregoing solar power system, the second housing is a molten salt storage tank.

In a further non-limiting embodiment of the foregoing solar power system, the molten salt circuit includes a first and second molten salt storage tanks.

In a further non-limiting embodiment of the foregoing solar power system, the second housing is separate from the first and second molten salt storage tanks, and is separate from the first housing.

In a further non-limiting embodiment of the foregoing solar power system, the oil and molten salt circuits each include a plurality of pipes and valves, and the valves are selectively adjustable to configure the oil and molten salt circuits for thermal energy charging and discharging conditions.

In a further non-limiting embodiment of the foregoing solar power system, the system further includes a controller, and the valves adjustable in response to the controller.

In a further non-limiting embodiment of the foregoing solar power system, the at least one heat exchanger includes two heat exchangers, and the valves are adjustable to direct the oil and molten salt circuits to a particular one of the two heat exchangers based on whether the solar power system is in a thermal energy charging or discharging condition.

A method of leak detection according to another exemplary aspect of the present disclosure includes, among other things, providing a solar power system including a concentrated solar receiver, an oil circuit, and a molten salt circuits. The method further includes establishing a flow of oil within the oil circuit, and establishing a flow of molten salt within the molten salt circuit. At least one heat exchanger is provided in communication with both the oil and molten salt circuits, and the at least one heat exchanger providing a double-layer boundary between the oil and molten salt. The at least one heat exchanger is monitored for a potential compromise in the double-layer boundary.

In a further non-limiting embodiment of the foregoing method of leak detection, the at least one heat exchanger includes two spaced-apart housings and at least one heat pipe.

In a further non-limiting embodiment of the foregoing method of leak detection, the method further includes providing at least one of the two spaced-apart housings and the heat pipe with a sensor.

In a further non-limiting embodiment of the foregoing method of leak detection, the monitoring step includes comparing, with a controller, a signal from the sensor with a predetermined threshold.

These and other features of the present disclosure can be best understood from the following drawings and detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings can be briefly described as follows:

FIG. 1 illustrates a solar power system during a thermal energy charging condition.

FIG. 2 illustrates the solar power system during a thermal energy discharging condition.

FIG. 3 illustrates an example heat exchanger for use in the solar power system.

FIG. 4 illustrates example heat exchangers for use in the solar power system.

FIG. 5 illustrates an example storage tank for use in a second embodiment of the solar power system.

DETAILED DESCRIPTION

FIGS. 1-2 illustrate an example solar power system 10 during thermal energy charging and discharging conditions, respectively. The example system 10 is generally known as a trough-type solar power plant. While a trough-type system 10 is illustrated, this disclosure extends to other systems, including central tower, or heliostat, power plants, as well as systems including combinations of troughs, heliostats and a central tower. Further, in some systems, the thermal energy charging and discharging conditions can occur simultaneously. As will be appreciated from the below, however, this disclosure has specific benefits in the context of systems which employ two fluids (e.g., oil and molten salt) which, when brought together, are reactive.

The example system 10 includes an oil circuit 12 and a molten, or solar, salt circuit 14. The oil circuit 12 includes pipes 16 and valves 18 a-e, which are selectively adjustable to direct oil flow in a particular manner. The oil circuit 12 is further in communication with concentrated solar receiver S, which in this example includes parabolic troughs 20 and a collector pipe 22. A thermodynamic cycle including a steam generator 24, turbine 26 and a generator 28 is located downstream of the troughs 20. The oil circuit 12 includes a pump P.

The molten salt circuit 14 includes a plurality of pipes 32 and valves 34 a-d. Like the valves 18 a-e, the valves 34 a-d are selectively adjustable to route molten salt between heat exchangers 30, 36, and first and second molten salt storage tanks 38, 40, respectively, as desired. In the illustrated example, the system 10 is arranged such that the first molten salt storage tank 38 receives and selectively stores hot molten salt, while the second molten salt storage tank 40 receives and selectively stores cold molten salt.

The valves 18 a-e and 34 a-d are selectively adjustable in response to a controller C to operate the system in different modes (or, conditions), as will be described below. In other examples, however, the valves 18 a-e and 34 a-d could be manually adjustable.

In this example, the oil circuit 12 includes five valves 18 a-e. A first valve 18 a is upstream of the concentrated solar receiver S, and allows selective bypass of the concentrated solar receiver S. A second valve 18 b is positioned downstream of the concentrated solar receiver to selectively tap heated oil that would otherwise be directed to the steam generator 24. A third valve 18 c is downstream of the steam generator to selectively direct relatively cold oil to a heat exchanger or the concentrated solar receiver S. Another valve 18 d is adjustable to direct oil to one of heat exchangers 30, 36. A fifth valve, 18 e, is selectively opened to prevent flow to the steam generator 24.

The molten salt circuit 14 includes valves 34 a, 34 c adjustable to allow entry of molten salt into the molten salt storage tanks 38, 40, respectively. Similarly, valves 34 b, 34 d are adjustable to release molten salt from the tanks 38, 40, respectively.

FIG. 1 is representative of a thermal energy charging condition (or, mode), during which an adequate amount of solar energy is available. In this condition, valve 18 a is configured to direct oil to the solar concentrator S. The troughs 20 reflect solar energy toward the collector tube 22 to heat the oil carried therein. The heated oil flows to the steam generator 24. The steam generator 24 generates steam to drive the turbine 26, which in turn drives the generator 28 to produce electricity. Via the valve 18 b, heated oil is tapped and routed to heat exchanger 30, by valve 18 d. The heat exchanger 30 is communication with both the oil circuit 12 and the molten salt circuit 14.

Via valve 34 d, the molten salt circuit 14 directs cold molten from the cold molten salt storage tank 40 to the heat exchanger 30 to absorb heat from the hot oil. The heated molted salt is then stored in the hot molten salt storage tank 38, by way of valve 34 a, for later use. While the steam generator 24 is operating in FIG. 1, valve 18 e could be partially opened, allowing for charging of the hot molten salt storage tank 38 with simultaneous operation of the steam generator 24.

In conditions where sunlight is inadequate or unavailable, as examples, the hot molten salt from storage tank 38 can be discharged in another mode of operation of the system 10 to transfer heat to the oil circuit 12. As illustrated in FIG. 2, the molten salt circuit 14 is arranged such that hot molten salt from the hot molten salt storage tank 38 is directed to the heat exchanger 36, via valve 34 b. Downstream of the steam generator 24, valves 18 c and 18 d direct relatively cold oil to the heat exchanger 36, where the cold oil absorbs heat from the hot molten salt. The heated oil is then directed to the steam generator 24, by way of valves 18 a and 18 b, to allow continued operation of the system 10.

While illustrated, valves 34 b and 34 d do not need to be included. For instance, flow through these valves could be regulated by operation of the pumps alone, while flow would generally be prevented by either gravity, shutting off the associated pumps, or a combination of the two.

FIG. 3 illustrates the detail of the heat exchanger 30, although it should be understood that FIG. 3 is also generally representative of the detail of the heat exchanger 36. The heat exchanger 30 includes at least one heat pipe 42 having ends 44, 46 disposed within first and second plenums 48, 50, respectively. In the illustrated example, the plenums 48, 50 are provided by separate housings 52, 54. As used herein, the term “ends,” as they relate to the ends 44, 46 of the heat pipe 42, includes the entire portion of the heat pipe 42 within the plenums 48, 50, respectively. That is, the side walls of the heat pipe 42 within the plenums 48 and 50 are considered “ends.” Further, the heat pipe 42 contains a working fluid F therein, and could optionally include a wick 56 for carrying condensed working fluid F between its ends. The working fluid F is non-reactive with oil and molten salt. Example working fluids are water, ethanol, acetone, sodium, and mercury.

The first and second plenums 48, 50 are in communication with the molten salt circuits 14 and the oil circuit 12, respectively. During a thermal energy charging condition, such as that illustrated in FIG. 1, the heat pipe 42 is provided with heat from the relatively hot oil, which is directed into the plenum 50 by way of the pipes 16. The hot oil heats the end 46 of the heat pipe 42. The working fluid F within the heat pipe 42 absorbs that heat through evaporation, and the hot working fluid F moves toward the opposite end 44 of the heat pipe 42.

Relatively cold molten salt enters the plenum 48 via the pipes 32, absorbs heat from the heat pipe 42, and then is directed toward the hot molten salt storage tank 38. The relatively cold oil is returned to the oil circuit 12, where it is re-heated. Then, the working fluid F condenses and moves toward the opposite end 46 of the pipe.

Because oil is a fuel, and molten salt is an oxidizer, the two may be reactive when brought together. Accordingly, the heat exchanger 30 includes two double-layer boundaries between the oil and the molten salt. A first of these double-layer boundaries is provided by a space 58 between the housings 52, 54. In this example, the space 58 is an axial space, relative to the longitudinal axis A of the heat pipe 42. A second double-layer boundary is provided by the closed ends 44, 46 of the heat pipe 42, as well as the arrangement of those ends 44, 46 within separate housings 52, 54.

Should one end 44, 46 of the heat pipe 42 be compromised, the other end of the heat pipe 42 would prevent mixing of the molten salt and oil. Likewise, should one of the housings 52, 54 be compromised, the other housing would prevent mixing between the molten salt and oil.

This arrangement of the heat pipe 42 between the spaced-apart housings 52, 54, provides the heat exchanger 30 with double-layer boundaries that effectively permit heat transfer between the molten salt and the oil.

Further, a leak detection system L (e.g., visual inspection, temperature sensors, pressure sensors, liquid detection, alarm circuits, etc) could be incorporated into the heat pipe 42, and/or the housings 52, 54 to detect a breach of the above-described double-layer boundaries. For example, these leak detection systems permit leak detection before compromise of the second layer of the double-layer boundaries occurs.

An example leak detection system L is shown in FIG. 4, including a leak detection controller 61 in communication with a plurality of sensors 63. The sensors 63 are coupled to the upper and lower plenums 52, 54 and the heat pipes 42 of the heat exchangers 30, 36. If one of the heat pipe 42 and the upper and lower plenums 52, 54 became compromised, a pressure and temperature within that particular component would change. In this example, the sensors 63 are temperature sensors, and the leak detection controller 61 is configured to identify a compromise in the heat exchangers 30, 36 when a signal from one of the sensors 63 passes a predetermined threshold. The leak detection system L could be configured to include pressure or temperature sensors 65, or liquid detection sensors 67. Further, any number of sensors 63 could be included in the leak detection system L.

While only one heat pipe 42 is shown in FIG. 3, the heat exchangers 30 and 36 could each include a multiple of heat pipes 42, as illustrated in FIG. 4. The heat exchangers in this application are not limited to any particular number of heat pipes 42.

While the housings 52, 54 of FIGS. 3-4 are separate structures from the storage tanks 38, 40, it is possible that the molten salt plenum could be provided by a storage tank 60, as shown in the example of FIG. 5. In FIG. 5, hot oil is routed to a plenum 62, provided by a housing 64. The molten salt within the molten salt storage tank 60 absorbs the heat from the hot oil via one or more heat pipes 42. Once the molten salt within the molten salt storage tank 60 is thermally charged, the oil circuit 12 can be rearranged such that heat from the molten salt storage tank is absorbed by the oil. The storage tank 60 can include an optional mixer 66, to increase the temperature consistency of the molten salt within the tank. While two storage tanks 38, 40 are illustrated in FIGS. 1-2, the molten salt circuit 14 could include any number of storage tanks, including only one storage tank, as represented by FIG. 5.

Although the different examples have the specific components shown in the illustrations, embodiments of this invention are not limited to those particular combinations. It is possible to use some of the components or features from one of the examples in combination with features or components from another one of the examples.

One of ordinary skill in this art would understand that the above-described embodiments are exemplary and non-limiting. That is, modifications of this disclosure would come within the scope of the claims. Accordingly, the following claims should be studied to determine their true scope and content. 

What is claimed is:
 1. A heat exchanger comprising: at least one heat pipe, the at least one heat pipe having a first end and a second end; a first housing including a first plenum, the first end of the at least one heat pipe within the first plenum; and a second housing including a second plenum, the second end of the at least one heat pipe within the second plenum, the second housing being spaced from the first housing to provide a double-layer boundary between the first plenum and the second plenum.
 2. The heat exchanger as recited in claim 1, wherein the first plenum is in communication with a first fluid, and wherein the second plenum is in communication with a second fluid different from the first fluid.
 3. The heat exchanger as recited in claim 2, wherein the first and second fluids are reactive when brought together.
 4. The heat exchanger as recited in claim 3, wherein the first fluid is oil and the second fluid is a molten salt.
 5. The heat exchanger as recited in claim 4, wherein the at least one heat pipe has a working fluid contained therein.
 6. The heat exchanger as recited in claim 5, wherein the working fluid is non-reactive with oil and molten salt.
 7. The heat exchanger as recited in claim 1, wherein the heat pipe has a longitudinal axis, and wherein first and second housings are spaced apart along the longitudinal axis of the heat pipe.
 8. The heat exchanger as recited in claim 1, wherein the first and second ends are closed ends.
 9. A solar power system comprising: a concentrated solar receiver; an oil circuit; a molten salt circuit; and at least one heat exchanger in communication with both the oil circuit and the molten salt circuit, wherein the at least one heat exchanger includes a first housing including a first plenum in communication with the oil circuit, and a second housing including a second plenum in communication with the molten salt circuit, wherein the first housing is spaced from the second housing to provide a double-layer boundary between the first plenum and the second plenum.
 10. The solar power system as recited in claim 9, wherein the at least one heat exchanger includes at least one heat pipe having a first end within the first plenum and a second end within the second plenum, wherein the first and second ends are closed ends.
 11. The solar power system as recited in claim 9, wherein the second housing is a molten salt storage tank.
 12. The solar power system as recited in claim 9, wherein the molten salt circuit includes a first and second molten salt storage tanks.
 13. The solar power system as recited in claim 12, wherein the second housing is separate from the first and second molten salt storage tanks, and is separate from the first housing.
 14. The solar power system as recited in claim 9, wherein the oil and molten salt circuits each include a plurality of pipes and valves, the valves selectively adjustable to configure the oil and molten salt circuits for thermal energy charging and discharging conditions.
 15. The solar power system as recited in claim 14, further including a controller, the valves adjustable in response to the controller.
 16. The solar power system as recited in claim 14, wherein the at least one heat exchanger includes two heat exchangers, the valves adjustable to direct the oil and molten salt circuits to a particular one of the two heat exchangers based on whether the solar power system is in a thermal energy charging or discharging condition.
 17. A method of leak detection, the method comprising: providing a solar power system including a concentrated solar receiver, an oil circuit, and a molten salt circuits; establishing a flow of oil within the oil circuit; establishing a flow of molten salt within the molten salt circuit; providing at least one heat exchanger in communication with both the oil and molten salt circuits, the at least one heat exchanger providing a double-layer boundary between the oil and molten salt; and monitoring the at least one heat exchanger for a potential compromise in the double-layer boundary.
 18. The method as recited in claim 17, wherein the at least one heat exchanger includes two spaced-apart housings and at least one heat pipe.
 19. The method as recited in claim 18, further including the step of providing at least one of the two spaced-apart housings and the heat pipe with a sensor.
 20. The method as recited in claim 19, wherein the monitoring step includes comparing, with a controller, a signal from the sensor with a predetermined threshold. 